The present invention is directed to photosensitive members or photoconductors useful in electrostatographic apparatuses, including printers, copiers, other reproductive devices, and digital apparatuses. In specific embodiments, the present invention is directed to photosensitive members having nano-size fillers dispersed or contained in one or more layers of the photosensitive member. The nano-size fillers, in embodiments, provide a photosensitive member with a transparent, smooth, and less friction-prone surface. In addition, the nano-size fillers, in embodiments, provide a photosensitive member with longer life, and reduced marring, scratching, abrasion and wearing of the surface. Further, the photoreceptor, in embodiments, has a reduced or eliminated deletion. Moreover, the photoreceptor provides an improved filler, which has good dispersion quality in the selected binder, and has reduced particle porosity.
Electrophotographic imaging members, including photoreceptors or photoconductors, typically include a photoconductive layer formed on an electrically conductive substrate or formed on layers between the substrate and photoconductive layer. The photoconductive layer is an insulator in the dark, so that electric charges are retained on its surface. Upon exposure to light, the charge is dissipated, and an image can be formed thereon, developed using a developer material, transferred to a copy substrate, and fused thereto to form a copy or print.
Many advanced imaging systems are based on the use of small diameter photoreceptor drums. The use of small diameter drums places a premium on photoreceptor life. A major factor limiting photoreceptor life in copiers and printers, is wear. The use of small diameter drum photoreceptors exacerbates the wear problem because, for example, 3 to 10 revolutions are required to image a single letter size page. Multiple revolutions of a small diameter drum photoreceptor to reproduce a single letter size page can require up to 1 million cycles from the photoreceptor drum to obtain 100,000 prints, a desirable goal for commercial systems.
For low volume copiers and printers, bias charging rolls (BCR) are desirable because little or no ozone is produced during image cycling. However, the microcorona generated by the BCR during charging, damages the photoreceptor, resulting in rapid wear of the imaging surface, for example, the exposed surface of the charge transport layer. More specifically, wear rates can be as high as about 16 microns per 100,000 imaging cycles. Similar problems are encountered with bias transfer roll (BTR) systems.
One approach to achieving longer photoreceptor drum life is to form a protective overcoat on the imaging surface, for example, the charge transporting layer of a photoreceptor. This overcoat layer must satisfy many requirements, including transporting holes, resisting image deletion, resisting wear, and avoidance of perturbation of underlying layers during coating. One method of overcoating involves sol-gel silicone hardcoats.
Another approach to achieving longer life has been to reinforce the transport layer of the photosensitive member by adding fillers. Fillers that are known to have been used to increase wear include low surface energy additives and cross-linked polymeric materials and metal oxides produced both through sol-gel and gas phase hydrolytic chemistries.
Problems often arise with these materials since they are often difficult to obtain in, or reduce to, the nano-size regime (less than 100 nanometers). Fillers with larger particle sizes very often are effective scatterers of light, which can adversely affect device performance. Also, dispersion in the selected binder then often becomes a problem. Even with suitably sized material, particle porosity can be a major problem as pores can act as traps for gases and ions produced by the charging apparatus. When this occurs the electrical characteristics of the photoreceptor are adversely affected. Of particular concern is the problem of deletion, a phenomenon that causes fogging or blurring of the developed image.
Japan Patent No. P3286711 discloses a photoreceptor having a surface protective layer containing at least 43 percent by weight but no more than 60 percent by weight of the total weight of the surface protective layer, of a conductive metal oxide micropowder. The micropowder has a mean grain size of 0.5 micrometers or less, and a preferred size of 0.2 micrometers or less. Metal oxide micropowders disclosed are tin oxide, zinc oxide, titanium oxide, indium oxide, antimony-doped tin oxide, tin-doped indium oxide, and the like.
U.S. Pat. No. 6,492,081 B2 discloses an electrophotographic photosensitive member having a protective layer having metal oxide particles with a volume-average particle size of less than 0.3 micrometers, or less than 0.1 micrometers.
U.S. Pat. No. 6,503,674 B2 discloses a member for printer, fax or copier or toner cartridge having a top layer with spherical particles having a particle size of lower than 100 micrometers.
U.S. patent application Ser. No. 10/379,110, U.S. Publication No. 20030077531 discloses an electrophotographic photoreceptor, image forming method, image forming apparatus, and image forming apparatus processing unit using same. Further, the reference discloses an electroconductive substrate, the outermost surface layer of the electroconductive substrate containing at least an inorganic filler, a binder resin, and an aliphatic polyester, or, alternatively, the outermost surface layer of the electroconductive substrate containing at least an inorganic filler and a binder resin and the binder resin is a copolymer polyarylate having an alkylene-arylcarboxylate structural unit.
U.S. patent application Ser. No. 09/985,347, U.S. Publication No. 20030073015 A1, discloses an electrophotographic photoreceptor, and image forming method and apparatus using the photoreceptor including an electroconductive substrate, a photosensitive layer located overlying the electroconductive substrate, and optionally a protective layer overlying the photosensitive layer, wherein an outermost layer of the photoreceptor includes a filler, a binder resin and an organic compound having an acid value of from 10 to 700 mgKOH/g. The photosensitive layer can be the outermost layer. A coating liquid for an outermost layer of a photoreceptor including a filler, a binder resin, an organic compound having an acid value of from 10 to 700 mgKOH/g and plural organic solvents.
Therefore, there exists a need in the art for an improved method of increasing wear of a photosensitive member. In addition, there exists a need for a photoreceptor surface with decreased susceptibility to marring, scratching, micro-cracking, and abrasion. In addition, there exists a need in the art for a photoreceptor with a transparent, smoother, and less friction-prone surface. Further, there exists a need for a photoreceptor that has reduced or eliminated deletion. Moreover, there is a need in the art for an improved filler which has good dispersion quality in the selected binder, and has reduced particle porosity.